There are a number of ways to do this, visionp.
Is it just one still image? Zoom into it on your timeline using the slider or by pressing the + key on your keyboard. By dragging the end of the still out further, you can extend its length, just like trimming a video clip. Using the timeline "ticker" you should be able to set it very precisely to whatever length you'd like.
As I said in your other thread, if you need help with some of these basic functions, have a look at my free Basic Training for Premiere Elements tutorials on Premiere Elements support site Muvipix.com. I also have a number of books available online that will show you in detail how to work with all of the tools in the program.
By click-dragging on either the Head, or the Tail of the still, with the Timeline zoomed in, you have Frame-accurate editing. If you need to increase the Duration by 3 Frames, just extend this by 3 ticks on the Timeline Ruler. You can also view this in the Info Panel (this is a Panel that I use all the time).
Awesome - thank you both of you. Learn something new every day!
But what's interesting to me still is there is no way to click on the image, then click properties and type in an exact duration. (For some reason I use this all the time in Premiere Pro)